The chemical and physical stabilities of a cathode active material are key factors affecting the electrochemical performance of a lithium ion battery. Today, developing highly stable cathode active material has been a research focus. When cathode active material is soaked in liquid electrolytes in the battery, the main metal ions in the cathode active material will dissolve easily, migrate away from the cathode and electrochemically deposit on the anode, which influences not only the stability and performance of the cathode active material but also sows the seeds of internal short-circuit. Surface coating of the cathode active material is a conventional method to solve this problem. However, the surface coating performance of the cathode active material is usually indirectly determined through the electrochemical performance test of the cathode or its lithium ion battery. This indirect determination not only takes a long period, but also cannot exclude influence from the lithium ion battery manufacture technology and other materials used in the battery. Therefore, the coating performance of the cathode active material cannot be determined accurately in practical application. A method of directly determining the surface coating performance of the cathode active material is to observe the coated cathode active material under a scanning electron microscope. However, this method is expensive, and only the area under the microscope can be analyzed, which does not objectively reflect the overall coating performance of the cathode active material.